Use the “oracle-database-server-12cR2-preinstall” package to perform all your prerequisite setup

Perpare Network

Change the setting of SELinux to permissiveby editing the "/etc/selinux/config" file, i
making sure the SELINUX flag is set as follows.
SELINUX=permissive
If you have the Linux firewall enabled, you will need to disable or configure it, as shown
here or here. The following is an example of disabling the firewall.

Potential Nameserver issues
Make sure the "/etc/resolv.conf" file includes a nameserver entry that points to the correct nameserver.
Also, if the "domain" and "search" entries are both present, comment out one of them. For the OS installation
my "/etc/resolv.conf" looked like this.
#domain localdomain
search localdomain
nameserver 192.168.1.1
The changes to the "resolv.conf" will be overwritten by the network manager, due to the presence of the
NAT interface. For this reason, this interface should now be disabled on startup. You can enable it manually
if you need to access the internet from the VMs. Edit the "/etc/sysconfig/network-scripts/ifcfg-enp0s3" (eth0)
file, making the following change. This will take effect after the next restart.
ONBOOT=no
Modify resolv.conf and reboot the system:
# Generated by Helmut
search example.com
nameserver 192.168.5.50
Afer a reboot we have following IP setting and Nameserver loopup should working fine
[root@ractw21 ~]# ifconfig
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether 08:00:27:c6:ab:10 txqueuelen 1000 (Ethernet)
enp0s8: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.5.141 netmask 255.255.255.0 broadcast 192.168.5.255
inet6 fe80::a00:27ff:fe83:429 prefixlen 64 scopeid 0x20<link>
enp0s9: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.2.141 netmask 255.255.255.0 broadcast 192.168.2.255
Note device emp0s3 has no IP V4 address assigned !
[root@ractw21 ~]# nslookup ractw21
Server: 192.168.5.50
Address: 192.168.5.50#53
Name: ractw21.example.comAddress: 192.168.5.141

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